International Advisory Board: James Archibald (Translation Studies) - Hugo de Burgh (Chinese Media Studies) - Kristen Brustad (Arabic Linguistics) - Daniel Coste (French Language) - Luciano Curreri (Italian Literature) - Claudio Di Meola (German Linguistics) - Donatella Dolcini (Hindi Studies) - Johann Drumbl (German Linguistics) - Denis Ferraris (Italian Literature) - Lawrence Grossberg (Cultural Studies) - Stephen Gundle (Film and Television Studies) - Tsuchiya Junji (Sociology) - John McLeod (Post-colonial Studies) - Estrella Montolío Durán (Spanish Language) - Silvia Morgana (Italian Linguistics) - Samir Marzouki (Translation, Cultural Relations) - Mbare Ngom (Post-Colonial Literatures) - Christiane Nord (Translation Studies) - Roberto Perin (History) - Giovanni Rovere (Italian Linguistics) - Lara Ryazanova-Clarke (Russian Studies) - Shi-Xu (Discourse and Cultural Studies) - Srikant Sarangi (Discourse analysis) - Françoise Sabban, Centre d'études sur la Chine moderne et contemporaine (Chinese Studies) - Itala Vivan (Cultural Studies, Museum Studies)
During lysosomal biogenesis, lysosomal proteins are transported in Mannose-6-Phosphate Receptor (M6PR)+ vesicles from the trans-Golgi Network to early and late endosomes for eventual incorporation into lysosomes 41. Disruption of M6PR+ vesicle trafficking can lead to a reduction in lysosome numbers 42 and altered localization of M6PR+ vesicles 43. In control iMNs (n=3 controls), M6PR+ vesicles were distributed loosely around the perinuclear region and to a lesser extent in the non-perinuclear cytosol (Supplementary Fig. 9a, b). In contrast, C9ORF72 patient (n=4 patients), C9ORF72+/−, and C9ORF72−/− iMNs frequently harbored densely-packed clusters of M6PR+ vesicles (Supplementary Fig. 9a, b). This was not due to a reduced number of M6PR+ vesicles in patient and C9ORF72-deficient iMNs (Supplementary Fig. 9c). Forced expression of C9ORF72 isoform B restored normal M6PR+ vesicle localization in patient (n=4 patients) and C9ORF72-deficient iMNs, confirming that a lack of C9ORF72 activity induced this phenotype (Supplementary Fig. 9a, b).
To confirm that glutamate receptor levels were increased on the surface of C9ORF72+/− and C9ORF72 patient iMNs, we used CRISPR/Cas9 editing to introduce a Dox-inducible polycistronic cassette containing NGN2, ISL1, and LHX3 into the AAVS1 safe-harbor locus of control, C9ORF72+/− and C9ORF72 patient iPSCs. This enabled large-scale production of iMNs that expressed motor neuron markers and had transcriptional profiles similar to 7F iMNs (Supplementary Fig. 11). Using this approach, we quantified the amount of surface-bound NR1 by immunoblotting after using surface protein biotinylation to isolate membrane-bound proteins. This confirmed that surface NR1 levels were higher on C9ORF72+/− and C9ORF72 patient iMNs (n=2 patients) than controls (n=3 controls)(Fig. 4e-h, Supplementary Fig. 5g, h).
IPSC-MNs at differentiation D35 were harvested in cold Hypotonic buffer (20 mM HEPES pH 7.4, 10 mM KCl, 2 mM MgCl2, 1 mM EDTA, 1mM EGTA, 1 mM DTT and protease inhibitor cocktail (Roche)) and lysed by passing through G25 needles 25 times and then spun down at 700 x g for 10min at 4℃. The Supernatant was loaded onto pre-made 30% Percoll solution and re-centrifuged at 33,000 RPM using Beckman rotor SWI55 for 50min at 4℃. 300 ul aliquots were taken from top to bottom as fractions and all the collected samples were boiled with SDS-PAGE sample buffer and analyzed by western blot.
iMNs were fixed in 4% paraformaldehyde (PFA) for 1h at 4 ºC, permeabilized with 0.5% PBS-T overnight at 4 ºC, blocked with 10% FBS in 0.1% PBS-T at room temperature for 2 h, and incubated with primary antibodies at 4 ºC overnight. Cells were then washed with 0.1% PBS-T and incubated with Alexa Fluor® secondary antibodies (Life Technologies) in blocking buffer for 2 h at room temperature. To visualize nuclei, cells were stained with DAPI (Life Technologies) then mounted on slides with Vectashield® (Vector Labs). Images were acquired on an LSM 780 confocal microcope (Zeiss). The following primary antibodies were used: mouse anti-HB9 (Developmental Studies Hybridoma Bank); mouse anti-TUJ1 (EMD Millipore); rabbit anti-VACHT (Sigma); rabbit anti-C9ORF72 (Sigma-Aldrich); mouse anti-EEA1 (BD Biosciences); mouse anti-RAB5 (BD Biosciences); mouse anti-RAB7 (GeneTex); mouse anti-LAMP1 (Abcam); mouse anti-LAMP3 (DSHB, cat. no. H5C6); rabbit anti-LAMP3 (Proteintech, cat. no. 12632); mouse anti-LAMP2 (DSHB, cat. no. H4B4); mouse anti-M6PR (Abcam, cat. no. Ab2733); rabbit anti-GluR1 (EMD Millipore, cat. no. pc246); mouse anti-GluR1 (Santa Cruz); rabbit anti-NR1 (EMD Millipore); mouse anti-NR1 (EMD Millipore, cat. no. MAB363); chicken anti-GFP (GeneTex).
To verify that PIKFYVE-dependent modulation of vesicle trafficking was responsible for rescuing C9ORF72 patient iMN survival, we tested the ability of a constitutively active RAB5 mutant to block C9ORF72 patient iMN degeneration. Active RAB5 recruits PI3-kinase to synthesize PI3P from PI and therefore, like PIKFYVE inhibition, increases PI3P levels 56. Constitutively active RAB5 did not improve control iMN survival (n=2 controls)(Supplementary Fig. 15k), but successfully rescued C9ORF72 patient iMN survival (n=3 patients)(Supplementary Fig. 15l). In constrast, dominant negative RAB5, wild-type RAB5, or constitutively active RAB7 did not rescue C9ORF72 patient iMN survival (n=1, 3, 3 patients, respectively)(Supplementary Fig. 14m-o).